KR20040002930A - Fuel cell or electrolyser construction - Google Patents

Abstract

The fuel cell or electrolyzer stack comprises a radial fuel and oxidant flow field that flows back to either side of the membrane electrode assembly.

Description

Fuel cell or electrolytic cell structure {FUEL CELL OR ELECTROLYSER CONSTRUCTION}

A fuel cell is a device that produces electricity directly by combining fuel and oxidant in a controlled manner. Since electricity is produced directly without intermediate combustion and generation steps, the electrical efficiency of a fuel cell is higher than when using fuel in a conventional generator. This is mostly well known. Fuel cells are thought to be simple and desirable, but many have studied for years until attempting to manufacture practical fuel cell systems.

Electrolyzers are effective in reversible fuel cells, where electricity is used to decompose water into hydrogen and oxygen. Both fuel cells and electrolyzers are thought to be an important part of the so-called "hydrogen saving". In the following, the reference is directed to a fuel cell, but it should be remembered to apply the same principle to the electrolyzer.

In mass production, one type of fuel cell is a so-called proton exchange membrane (PEM) fuel cell (sometimes called polymer electrolytes or solid polymer fuel cells (PEFCs)). Such cells contain an electrically insulating (but ion conducting) polymer membrane that uses hydrogen as fuel and has porous electrodes disposed on both sides. The membrane is typically a fluorosulfonate polymer and the electrode typically contains a noble metal catalyst dispersed in a carbonaceous powder substrate. Such an electrode and membrane assembly is commonly referred to as a membrane electrode assembly (MEA).

Fuel (typically hydrogen) is supplied to an electrode (anode) that is oxidized to release electrons to the anode and to release hydrogen ions to the electrolyte. An oxidant (typically air or oxygen) is supplied to another electrode (cathode), where electrons from the cathode combine with oxygen and hydrogen ions to produce water. Subclassed proton exchange membrane fuel cells are direct methanol fuel cells in which methanol is supplied as fuel. In this invention, it is intended to cover another fuel cell using such a fuel cell actual proton exchange membrane.

In conventional PEM fuel cells, many of these membranes are separated and stacked together by flow field plates (also called bipolar plates). In general, flow field plates are formed of metal or graphite to allow electrons to move well between the anode of one film and the cathode of an adjacent film.

Flow field plates have grooves on their surfaces to supply fluid (fuel or oxidant) and to remove water produced as a reaction product of a fuel cell. Various methods of making grooves have been described, for example, it has been proposed to form such grooves by machining, embossing or forming (WO 00/41260) and sandblasting (WO 01/04982) through a resist. In a sand blasting system, particles (such as sand, grit, fine beads or freezing material) are shot with air blowing towards the article to be treated.

In order for the fluid to be evenly distributed on their respective electrode surfaces, a so-called gas diffusion layer (GDL) is placed between the electrode and the flow field plate. The gas diffusion layer is a porous material, and is generally made of carbon paper or cloth having a layer of carbon powder adhered to one side and coated with a hydrophobic material to promote the rejection of water.

Fuel and oxidant flow fields are typically wavy, extending from the fluid inlet manifold to the fluid outlet manifold. However, other flow field shapes may be used. In some descriptions (for example, US5773160, US6087033, and US-A-2001 / 0005557), one side of the membrane electrode assembly provides a countercurrent arrangement in which the oxidant moves to fuel in the opposite direction to the other side of the membrane electrode assembly. It aims at description. These arrangements do not provide full backflow of fluid flow, but provide an asymmetric distribution of pressures that can cause operational problems (described below).

The present invention relates to a fuel cell and an electrolytic cell, but is not particularly limited, and is applicable to a proton exchange membrane fuel cell and an electrolytic cell.

1 schematically shows a partial cross-sectional view of a stack;

2 schematically illustrates a side view of several stacks according to FIG. 1 embedded in a room;

3 schematically shows a plan view of several stacks according to FIG. 1 embedded in a room;

4 schematically shows a top view of a fluid flow plate for use in accordance with the present invention;

5 schematically illustrates a bottom view of the fluid flow plate of FIG. 4;

6 is a schematic view of a pair of fluid flow plates incorporating a sealing mechanism in accordance with the present invention;

7 is a variant of the flow field plate used in accordance with the present invention.

Applicants have found that this problem can be overcome by providing radial divergence / convergence flow fields of fuel and oxidant flow fields in the sense that one flow field diverges outward and the other flow fields converge inward. Accordingly, the present invention provides a fuel cell or electrolyzer assembly having a fuel and oxidant flow field in a radial direction that is countercurrent to either side of the membrane electrode assembly.

This arrangement further has the advantage of reducing the number of fluid connections. One advantageous arrangement is that the first reactant gas flows outwardly from the manifold in the fuel cell stack to the first reactant exit and the second reactant gas flows inwardly from the edge of the flow field to the second reactant exit.

Illustrative examples of the present invention with reference to the drawings are as follows:

Stack 1 (FIG. 1) includes a plurality of fluid flow plates 2. The fluid flow plate is aligned with an opening 403 (FIGS. 4 and 5) that forms a fuel supply opening 3. One end of the stack is terminated by an end plate 4 containing electrical connectors 5. The end plate 4 seals the distal end of the fuel supply opening 7. The stack is fuel outlet 6; Oxidant outlet 7; It has a connection which acts as a coolant inlet 8 and a coolant outlet 9.

Some stacks 1 include a fuel outlet 6; Oxidant outlet 7; It is provided in the room 101 which has the system of the manifold 102 connected to the coolant inlet 8 and the coolant outlet 9. In addition, the room 101 has an electrical connection system 103 connected to the laminated electrical connector 5. The electrical connection system that forms part of the manifold 102 system connects to the underside of each stack. The room 101 and the stack 1 are bounded by a void space 104 therebetween.

The flow field plate 2 is annular as described above and has a central opening 403. The fuel inlet 404 leads from the opening 403 to the humidifier 407. From the humidifying part 407 the flow field 408 is directed to the fuel outlet 405 (only the flow field part is shown, and some channels extend radially outwards in the humidifying part). The opening 49 passes through the flow field plate 1 and the openings 409 aligned in the stack form a way out to guide the surplus fuel to the fuel outlet 6.

Land 406 is disposed to accommodate the seal, which may occur in the formation of a flow field or in a separation step.

The oxidant flow field on the bottom surface of the flow field plate 2 is located opposite to the oxidant flowing in the radially inward direction from the outer edge of the flow field plate 402 to the inner outlet 407 which contacts the opening 410. The openings 410 aligned in the stack form an escape route that guides the excess oxidant to the oxidant outlet 7. Coolant channel 411 serves as coolant outlet opening 413 at coolant inlet opening 412. The coolant inlet opening 412 aligned at the adjacent plate receives coolant from the coolant inlet 8 and the coolant outlet opening 413 aligned at the adjacent plate directs the coolant to the coolant outlet 9.

The coolant channel 411 is arranged to be located in the humidifying part 407 opposite the adjacent flow field plate. A water permeable membrane may be placed between the coolant channel 411 and the humidifying channel 407 to humidify it. Sufficient humidification is required to prevent the membrane from drying.

Similar arrangements can be used to humidify the incoming oxidant using coolant tracks on the fuel side of the opposing flow field plate. The need for humidification on the oxidant side is less than on the fuel side because water is generated on the oxidant side of the membrane electrode assembly. Some humidification of the oxidant is necessary (to prevent the loss of water in the area where the oxidant enters the membrane), but too much humidification is undesirable because this limits the water soluble capacity of the oxidant.

The water permeable membrane can be made of, for example, thin film silicone rubber, and the membrane of the membrane electrode assembly can be used for this role.

The pressure of the oxidant in the void space 104 is compressed down the stack in the direction of arrow "A" in FIG. The gas pressure in the stack compresses the stack outward in the direction "B" which tends to separate the stack plates. The compressive force in direction "A" acts the opposite of the gas compression in direction "B." The proper choice of actual pressure and area can make the stack under compression. Of course, it can also be used for single lamination in a room.

Of course, the overall arrangement can be reversed (an oxidant in the middle and a fuel on the outside) but the arrangement shown is preferred for safety reasons.

The described and illustrated arrangement is not limited to circular flow field plates, although the general flow field plates are rectangular, which causes problems with sealing at the corners. The circular or oval geometry of the seal is advantageous. Circular arrangements are not ideal for alignment, but hexagonal plates may generally be used to secure holes in the corners that are provided with means to align or secure threaded rods or other stacks as shown in FIGS. 4 and 5. However, relatively light safety measures can be used since the gas pressure in the stack is at least partially compensated for by the stack external pressure.

The radial gas flow arrangement of FIGS. 4-6 is advantageous for several reasons. First, one has a countercurrent flow between the fuel and the oxidant that crosses the membrane electrode and maintains a relatively even pressure differential when compared to a conventional bipolar that tends to have a crossflow arrangement. This relatively even pressure differential means that the membrane is under relatively reduced stress. Second, the pressure is more evenly distributed across the lamination width, which means that the force acting on the bipolar plate is distributed evenly while reducing the risk of plate breakage or demoulding. Moreover, the equality of the pressure distribution leads to an improvement in the uniformity of electricity generation across the membrane electrodes.

FIG. 7 illustrates another form of radial backflow flow field dipolar, where flow field plate 702 is a hexagonal annulus with fuel supply opening 703. A fuel supply opening 703 is connected to the fuel outlet 705 leading to the fuel outlet 708 in the branch flow field shape 704 (partially shown). Land 706 is arranged to receive the seal, which placement takes place in the formation of a flow field or in a separation step.

The oxidant flow field with respect to the adjacent flow field plate is opposite to the oxidant flowing from the outer edge of the flow field plate to the internal outlet communicating with the oxidant outlet 709. Opposite the oxidant flow field plate is a coolant track. The coolant inlet hole 711 passes through the coolant track to the coolant outlet hole 712.

In this arrangement, the fuel flow diverges and the oxidant flow converges to provide a radial fluid flow that flows back to each side of the membrane electrode (meaning to move or radiate towards a point, and to limit the radius of the circle). Use "radial" as otherwise). Preferred plate materials include graphite, carbon-carbon composites or carbon-resin composites. However, the present invention is not limited to these materials, and any material having suitable physical properties can be used.

The above-described classification constants and combinations can form the present invention in their own context.

Claims (3)

A fuel cell or electrolyzer assembly having a radial fuel and oxidant flow field countercurrent to either side of the membrane electrode assembly. The fuel cell or assembly of claim 1, wherein the first reactant gas flows radially inward from the manifold to the first reactant outlet and the second reactant gas flows inward from the edge of the assembly to the second reactant outlet. 3. The fuel cell or electrolyzer assembly of claim 1 or 2, wherein the gas entering the flow field plate advances the seal ring toward the sealing groove on the adjacent flow field plate maintained at a relatively low pressure with respect to the incoming gas.